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<Title> GATOR </Title>
<H1>GATOR</H1>

<P> This work is part of an <!WA0><a href = "http://www.netlib.org/nse/home.html">
HPCC </a> project funded by 
<!WA1><a href = "http://www.netlib.org/nse/curr_hpcc.html"> NASA </a>  to develop a
state-of-the-art Earth System Model (ESM) that will be comprised of a coupled
atmosphere and ocean system including chemical tracers
that are found in, and may be exchanged between, the atmosphere
and the oceans.  The starting point of the ESM model is the
<!WA2><a href = "http://www.atmos.ucla.edu/~vwk206/esm.html"> UCLA AGCM</a>, 
which has been parallelized on different platforms and
will be coupled with GATOR, a Gas, Aerosol, Transport, and
Radiation Chemistry model, developed by M. Jacobson, O. Toon, R. Turco, 
and R. Lu.  The UCLA ESM model will archive and retrieve 
model output via the
<!WA3><a href = "http://s2k-ftp.cs.berkeley.edu:8000/cgi-bin/imagemap/s2khome?357,117"> Sequoia </a> database.  

Coupled systems are an important tool for helping scientists
to understand complex phenomena
such as El Nino and stratospheric ozone depletion.  


<P>
A parallel version of GATOR is being developed at Berkeley by
<!WA4><a href = "http://http.cs.berkeley.edu/~demmel"> Jim Demmel</a>
and <!WA5><a href = "http://http.cs.berkeley.edu/~ssmith"> Sharon Smith </a>.
GATOR models
atmospheric chemistry in the Los Angeles Basin, and has been used for
detailed air pollution studies.  Our task is to parallelize GATOR and
scale it to the globe.

<P>
GATOR includes
both gases and aerosols, modeling
<DL>
<DD>gas-phase chemistry; 
<DD>aqueous-phase chemistry; 
<DD>radiation transfer;
<DD>aerosol nucleation, coagulation, growth and evaporation; 
<DD>horizontal advection and vertical convection;
<DD>dry and wet deposition; 
<DD>visibility and emissions. </DL>
<P>

<H2> The Parallel Version of GATOR </H2>

<P>
A primary motivation for this research is to provide 
atmospheric scientists
with  the best computational means to further their studies of the
earth's future climate.  Since the UCLA ESM is still evolving,
it is important that the codes also be portable, so our efforts  
are thus focused on developing portable, parallel code that
can be performance tuned for different parallel architectures.

<P>
The main challenges in parallelizing GATOR are
overcoming problems due to load imbalance and minimizing 
the communication costs.   The figure below shows
the differences in computation that can result in load
imbalance:


<P><A NAME=205>&#160;</A><A NAME=Figglob>&#160;
</A><!WA6><IMG  ALIGN=BOTTOM ALT="" SRC="http://http.cs.berkeley.edu/~ssmith/SC95/SP2_Load_3d.gif">

<P>
In the picture,
the z-axis shows time, while the x and y axis show the
latitudinal and longitudinal partitioning of the atmosphere into
block columns.  
Each processor owns one set of block columns.  The
difference in time among the processors illustrates the amount
of computation due to solving ODEs that arise from chemical
kinetic equations.  The largest amount of computation occurs in
parts of the globe that are in the summer and daylight, 
whereas the processors holding atmospheric cells in winter and night     
require the least amount of computation.  Click <!WA7><a href = "http://http.cs.berkeley.edu/~ssmith/world.gif">
here</a> to see the ODE solver computation costs for the world.

<P>
Our solution to the load balancing problem is to use a block-cyclic
layout which will collect different atmospheric cells from the 
different parts of the globe together in a single processor.  The
hope is that each processor will have cells requiring 
different amounts of computation, but not all of the computationally
intensive cells at once.   The pictures below illustrate a block
layout, which does not prevent against load imbalance, and a 
block-cyclic layout.

<P><A NAME=204>&#160;</A><A NAME=Figpipeline>&#160;</A>
<!WA8><IMG  ALIGN=BOTTOM ALT="" SRC="http://http.cs.berkeley.edu/~ssmith/mapping_all.gif">

<H2>Performance Modeling and the ESM</H2>

Throughout the design of the parallel implementation of GATOR,
we used a timing model to help choose between different
design alternatives that would benefit GATOR both as a stand-alone
system and as part of the UCLA AGCM.
The results of this work are reported in: 

<P>
<DL>
<DT><A NAME=DemmelSmith><STRONG></STRONG></A><DD>
J. Demmel and S. L. Smith.
<!WA9><a href="http://http.cs.berkeley.edu/~ssmith/shpcc.ps">
Parallelizing a global atmospheric chemical tracer model</a>.
In <em> Proceedings of the Scalable High Performance Computing
Conf.</em>, pages 718--725, Knoxville, TN., May 1994.
</DL>

<P>
<DL>
<DD>J. Demmel and S. L. Smith.
<!WA10><a href="http://http.cs.berkeley.edu/~ssmith/SC95/paper.html"> 
Performance of a parallel global atmospheric chemical tracer model.</a>
Submitted to <em> Supercomputing 95 </em>.
</DL>
<P>

<H2>EOSDIS</H2>
<p>
We are extending our modeling effort to help explore an architecture
for the <!WA11><A HREF="http://eos.nasa.gov"> Earth Observing System (EOS)</a>. This  
effort is part of <!WA12><A HREF="http://epoch.CS.Berkeley.EDU:8000/nasa_e2e/">
"End-to-End Problems in EOSDIS"</A>, a NASA-sponsored multi-year project
to investigate alternative data management strategies for the EOS. 
The project involves researchers at 
the 
<!WA13><a href="http://http.CS.Berkeley.EDU">Berkeley</a>, 
<!WA14><a href="http://www.cs.ucla.edu">Los Angeles</a>,
<!WA15><a href="http://www-cse.ucsd.edu:80/users/pasquale/ResearchProjects/EOSDIS.html"
>San Diego</a>, and 
<!WA16><a href="http://www.icess.ucsb.edu/eosdis/eosdis.html">Santa Barbara</a>
campuses of the University of California. 

<p>
For some sample views of environmental and climate data,
courtesy of <!WA17><a href="http://www.icess.ucsb.edu/eosdis/eosdis.html">
Jeff Dozier</a> at UC Santa Barbara, click
<!WA18><a href="http://http.cs.berkeley.edu/~ssmith/colorfigs.ps"> here</a>.

<HR>
last updated on December 12, 1995.
<ADDRESS>ssmith@CS.Berkeley.EDU</ADDRESS>
